The present invention relates to a flying spot scanning system for communicating video information to a scanned medium, and more particularly to a scanning system comprising a rotating polyhedron mirror for controlling a scanning laser beam.
Recently, improved recording devices called "laser printers" have been gaining popularity and have been meeting with commercial success. The major function of "laser printers" is importing visual data such as letters and pictures etc. derived from a computer, a word processor, a facsimile device etc. to a scanned medium in the form of an electrostatic charge pattern. A laser beam functions as scanning light.
An example of the "laser printers" is disclosed in Starkweather, U.S. Pat. No. 4,034,408 issued July 5, 1977, entitled "Flying Spot Scanner". The disclosure of this patent is incorporated herein by reference. However, in the conventional laser printers, a He-Ne gas laser is provided in which case an acousto-optical modulator is needed for modulating a laser beam in conformance with video signal information as disclosed in U.S. Pat. No. 4,034,408. The provision of the acouto-optical modulator resulted in loss of the laser beam when a laser device with a high intensity laser beam is needed.
To eliminate the need for such a modulator, a conventional laser printer comprising a semiconductor laser diode has been investigated. The conventional laser printer requires a collimating lens, a beam expander lens and an f-.theta. characteristics imaging lens (f: focal length .theta.: inclination angle) which are very costly to thereby make the laser printer expensive and often impractical.
Thus, it is desired to develop at a practicable cost laser printer comprising the semiconductor laser diodes.